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Lightning is a big spark of electricity caused by a build-up of electric charge in clouds. The spark passes between clouds or from the cloud to the ground.
In 1752, the famous scientist William Franklin conducted an experiment to find out if lightning was electricity. He flew a homemade kite, with a wire attached to it, into a rain cloud. Franklin expected the lightning to strike the wire, and flow down the kite string to a key tied near the end. If all worked, he expected to get a spark when the key was touched. It worked, and Franklin had been very lucky. Had the lightning strike been any stronger, he could have been badly hurt or killed. After this and other experiments, Franklin invented lightning rods to protect buildings from lightning strikes.
A lightning flash can happen in half a second. In that instant, the lightning flash heats the surrounding air to 33,000 degrees celcius - five times hotter than the surface of the sun - and produces about 100 million volts of electricity! The intense heat causes thunder.
Fact
The word 'electricity' comes from the Greek word for amber.
The ancient Greeks noticed that when amber was rubbed with cloth, small objects would cling to it.